Extra Questions On Class 10 Science Chemical Reactions and Equations
Q.1. In electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode?
AnswerAnswer: It is because water contains hydrogen and oxygen in the ratio of 2 : 1.
Q.2. Balance the following chemical equations.
(PbNO3)2 →PbO + NO2 + O2
AnswerAnswer: 2(PbNO3)2 → 2PbO + 4NO2 + O2
Q.3. What happens chemically when quicklime is added to water filled in a bucket?
AnswerAnswer: Quicklime reacts with water to form slaked lime and produces lot of heat and hissing sound.
Q.4. On what basis is a chemical equation balanced?
AnswerAnswer: A chemical reaction is balanced on the basis of law of conservation of mass.
Q.5. What change in colour is observed when white silver chloride is left exposed to sunlight? State the type of chemical reaction in this change.
AnswerAnswer: Silver chloride becomes grey. It is a photochemical decomposition reaction.
Q.6. Write a balanced chemical equation for the reaction between sodium chloride and silver nitrate indicating the physical state of the reactants and the products.
Q.7. State one basic difference between a physical change and a chemical change.
AnswerAnswer: In physical change, no new substance is formed, whereas in a chemical change, new substance(s) is/are formed.
Q.8. What is meant by a chemical reaction?
AnswerAnswer: The reaction representing a chemical change is called a chemical reaction.
Q.9. AgN03(aq) + NaCl(aq)——————–> AgCl(s)4↓ + NaN03(aq)
FeS + H2S04————> FeS04 + H2S↑
Consider the above mentioned two chemical equations with two different kinds of arrows (↑and ↓) along with product. What do these two different arrows indicate?
AnswerAnswer: ↑ shows the gas is evolved whereas ↓ shows insoluble substance (precipitate) is formed.
Q.10. Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water which is a compound made up of hydrogen and oxygen is used to extinguish fire. Why?
AnswerAnswer: It is because properties of compound (H2O) are different from properties of its constituting elements, i.e. H2 and O2.
Q.11. Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change?
It is decomposition reaction.
Q.12. What is an oxidation reaction? Give an example of oxidation reaction. Is oxidation an exothermic or an endothermic reaction?
AnswerAnswer: The reaction in which oxygen or electronegative element is added or hydrogen or electropositive element is removed or loss of electrons takes place, is called an oxidation reaction, e.g. ,
Oxidation reactions are mostly exothermic in nature because heat is evolved in this process.
Q.13. Describe an activity to demonstrate the change that takes place when white silver chloride is kept in sunlight. State the type of chemical reaction which takes place.
AnswerAnswer: Aim: To demonstrate the change that takes place when white silver chloride is kept in sunlight.
Materials Required: AgNO3(aq), NaCl(aq), test tubes.
1. Take 5 ml of silver nitrate solution in a test tube.
2. Prepare sodium chloride solution in another test tube.
3. Add sodium chloride solution into test tube containing silver nitrate solution.
4. Observe the colour of silver chloride formed chloride to grey silver metal Dry it with the help of filter papers and place it on the watch glass.
5. Place the watch glass under sunlight for sometime.
6. Observe the colour of the silver chloride after sometime. Observation: White silver chloride turns grey in sunlight because silver metal is formed.
Explanation: Silver chloride is photosensitive. It decomposes in presence of sunlight to form silver metal and chlorine gas.
Conclusion: Decomposition of silver chloride in presence of sunlight is photochemical decomposition reaction.
Q.14. When magnesium ribbon burns in air or oxygen, a product is formed. State the type of chemical reaction and name the product formed in the reaction. Write balanced chemical equation of this reaction.
The type of reaction is combination reaction and the product formed is magnesium oxide.
Q.15. Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions.
Displacement reaction is a reaction in which more reactive metal can displace less reactive metal from its salt solution.
Double displacement reaction are those reactions in which compounds exchange their ions to form two new compounds (i) Double displacement reaction (ii) Displacement reaction
Q.16. When you have mixed the solutions of lead(II) nitrate and potassium iodide,
(i) what was the colour of the precipitate formed and can you name the precipitate?
(ii) write the balanced chemical equation for this reaction.
(iii) is this also a double displacement reaction?
AnswerAnswer: (i) The colour of the precipitate is yellow. The name of compound formed as a precipitate is Pbl2 (lead iodide).
(iii) Yes, it is also a double displacement reaction.
Q.17. What do you mean by exothermic and endothermic reactions? Give examples.
AnswerAnswer: Exothermic reactions are those in which heat is evolved, e.g.
Endothermic reactions are those reactions in which heat is absorbed, e.g.
Q.18. What happens when an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride? State the physical conditions of reactants in which the reaction between them will not take place. Write the balanced chemical equation for the reaction and name the type of reaction.
AnswerAnswer: White precipitate of barium sulphate is formed.
If both reactants are in solid state, then the reaction will not take place between them.
It is a double displacement as well as a precipitation reaction.
Q.19. What is a redox reaction? When a magnesium ribbon burns in air with a dazzling flame and forms a white ash, is magnesium oxidised or reduced? Why?
AnswerAnswer: The reactions in which oxidation (loss of electrons) and reduction (gain of electrons) take place simultaneously are called redox reactions.
Magnesium is getting oxidised because it is losing electrons to form Mg2+ and oxygen is gaining electrons to form O2-, therefore it is getting reduced.
Q.20. Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.
AnswerAnswer: Any two of these observations will suggest chemical reaction has taken place.
(i) Change in state.
(ii)Change in colour.
(iii) Evolution of gas.
(iv)Change in temperature.
For example, lead nitrate is white crystalline solid which on heating gives yellowish brown solid (lead monoxide). A brown gas and a colourless gas is also evolved. It shows chemical reaction has taken place.
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